The present invention relates in general to vegetation trimmer apparatus and in particular to vegetation trimmer apparatus having flexible cutting members.
Internal combustion engine and electric motor powered vegetation trimmers are commonly used to cut and trim grass, weeds, brush and other vegetation. The typical motorized trimmer comprises an elongate handle which to which is connected an internal combustion or electric motor which rotatably drives a trimmer head located at a distal end of the handle. The trimmer head, in turn, carries one or more radially outwardly projecting cutting members or blades which cut the vegetation as the trimmer head rotates. In heavy duty internal combustion trimmers, the trimmer head may include one more flexible or rigid cutting means. If rigid, the cutting means assume the form of blades fabricated from plastic and/or metal and often having corrugations about their peripheral cutting edges. The blades are pivotally attached to the trimmer head such they yield when they contact hard objects, thereby prolonging the service lives of the blades. Rigid blades are normally used to cut very dense vegetation and may cause considerable injury to the trimmer operator or other persons should they accidentally be struck by the blades during operation of the trimmer.
In lighter duty electric trimmers, the cutting means may be fabricated as a continuous strand flexible monofilament plastic line wrapped about a spool contained within the trimmer head. In such devices, the plastic line is typically selectively dispensed by the centrifugal force generated by rotation of the trimmer head. A disadvantage common to these sorts of devices is that the line frequently becomes jammed when a user attempts to dispense fresh line from the spool. When this occurs, the user must stop the trimming operation, disassemble the trimmer head, fix the jam and reassemble the trimmer head before resuming trimming. Such repeated disruption can be quite frustrating and time-consuming.
Recently, some vegetation trimmers have come to employ finite lengths of monofilament plastic line or string that can be quickly and easily replaced as they become broken or worn without need to resort to disassembly and reassembly of the trimmer head. Each of these designs uses a one-way gripping means that permits withdrawal of a worn or broken string from a central portion of the trimmer head and insertion of a new replacement string through a peripheral wall of the trimmer head to replace the old string. Once inserted into the trimmer head, the one-way gripping means resists withdrawal of the new string in the direction opposite that to which it was inserted into the trimmer head. More particularly, when a new length of trimmer string is inserted through the peripheral wall of the trimmer head it engages a pivotable cam gripping member. The user then continues insertion of the string until a desired length of the string projects from the periphery of the trimmer head for vegetation cutting purposes. When the user releases the string, the cam is biased by a spring into gripping contact with the string. And, when the user reactivates the device, the rotation of the trimmer head generates centrifugal force that enhances the gripping force of the cam. Examples of such devices are provided in U.S. Pat. Nos. 5,758,424; 5,887,348; 5,896,666 and 6,347,455.
Although generally suitable for their intended purposes, the gripping means disclosed by these patents, which employ torsion or tension springs to bias the pivoted cams, constitute an arrangement that is unduly complex in design and less than desirable in terms of cost and ease of manufacture.
An advantage exists, therefore, for a vegetation trimmer apparatus including a rotatable trimmer head for receiving at least one finite length of replaceable trimmer string that is releasably engageable by one-way gripping means of simple design and construction that is economical to manufacture, long-lasting, and adaptable to a wide variety of trimmer head designs.
Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds.
The present invention provides a motorized vegetation trimmer apparatus comprising an elongate main handle to which is connected an internal combustion or electric motor that rotatably drives a trimmer head located at a distal end of the handle. The trimmer head, in turn, carries one or more radially outwardly projecting cutting means which cut the vegetation as the trimmer head rotates. The trimmer apparatus preferably includes a steering handle attached to
the main handle to facilitate guidance of the apparatus during operation.
The cutting means comprises at least one finite length of pliant strand or string. The pliant strand is preferably flexible monofilament plastic of a type used in conventional vegetation trimmer apparatus, e.g., nylon or the like. The cutting means is releasably gripped by one-way gripping means including a reciprocating gripping member and a compression spring that biases the gripping member into gripping contact with the string. The gripping means are uncomplicated in design, reliable in operation, comparatively inexpensive and simple to manufacture, and readily adaptable to a wide variety of trimmer head designs.